The present invention relates to a video signal processing device for a television receiver or the like, which processes scanning lines by converting them into a doubled speed form in an in-field processing.
The conventional video signal processing device in which scanning lines are converted into a doubled speed by an in-field processing comprises, as shown in FIG. 1, a delay circuit 300 for receiving a video signal Si to produce a delayed real line signal Sa, and an interpolation filter 400 for receiving the video signal Si to produce an interpolated signal Sb.
The interpolation filter 400 serves to produce the interpolated signal Sb on the basis of each of video signals in a vertical, a horizontal and an oblique direction, and is composed of a plurality of line memories, coefficient multipliers, adders, etc.
An example of such conventional interpolation filter 400 is shown in FIG. 2. Its operation is as follows. The video signal Si is delayed by line memories 402.about.404 by one line each successively, and each of the video signal and the delayed video signals is multiplied by each of the coefficient multipliers 405, 406, 407, and 408. The video signals with the coefficients having been applied by the coefficient multipliers 405, 406, 407 and 408 are added by an adder 409, whereby an interpolated signal Sv is produced on the basis of the video signal in the vertical direction. The interpolated signal Sv thus obtained is delayed by a plurality of D-type flip-flops 410, 411, 412 and 413 in the horizontal direction, successively, and each of the signal Sv and the resultant delayed signals is multiplied by each of corresponding coefficient multipliers 414, 415, 416, 417 and 418. The interpolated signals having been subjected to multiplication by the respective coefficient multipliers 414.about.418 are added by an adder 419, thereby producing the interpolated signal Sb. If the real line signal Sa obtained by delaying the video signal Si by the delay circuit 300 and the interpolated signal Sb are alternately outputted for each scanning line, an output of the doubled-speed converted scanning lines can be obtained.
However, the conventional video signal processing device has the following defect. When the scanning lines are converted into a double speed form in the in-field processing, the interpolated signal is produced by one interpolation filter. For this reason, if such an interpolation filter that produces an interpolated signal having a slanting and smooth edge is used for the processing of a fine picture pattern, the image is distorted or broken up at a high frequency region resulting in a blurred image, thus deteriorating the horizontal resolution thereof.